1. Field of the Invention
The present invention relates to a hot isostatic pressing apparatus (HIP apparatus) for economically performing a treatment of a large quantity of products capable being carried under the atmospheric pressure in the heated state such as Al cast products Mg cast products or the like and whose hot isostatic pressing treatment (HIP treatment) temperature is not more than 600° C., and particularly to a method and apparatus wherein two high-pressure vessels are combined and operation is carried out whereby pressing and pressure reducing are carried out in a short period of time to realize shortening of cycle time and to improve economic properties of the HIP treatment.
2. Description of the Related Art
The problem on industrial popularization of the HIP treatment of cast pieces of light-alloy metal materials such as Al and Mg which are objects of the present invention basically lies in economic properties, that is, treatment costs. In the cost of the HIP treatment, the treatment cost is very high due to long cycle time. The present invention aims at shortening the cycle time and improvement of economic properties resulting from improvement of apparatus utilizing efficiency. The related art proposed to improve the HIP treatment technique from a viewpoint of the foregoing and the problem thereof will be explained hereinafter.
A compressor for pressing a pressure medium gas, a reducing device for reducing pressure, and various valves are also expensive. There has been also proposed a method in which a pressing and reducing system constituted of these (expensive) parts is by 20 to 40% in operating time at one cycle, and therefore, a plurality of high-pressure vessels are connected to the pressing and reducing system, and operation is carried out so as to shift an operating phase to reduce stop-time of the compressor whereby the apparatus price is relatively reduced (see FIG. 12, Japanese Patent Publication No. 23484/1995).
The above-proposed HIP apparatus 67 comprises, as shown in FIG. 12, two high-pressure vessels 68, and a pressing/reducing system 72 provided with a gas cylinder 69, a gas compressor 70, a reducing device 71 and many valves, whereby the start time of cycle motion in the high-pressure vessels 68 is shifted. When in one high-pressure vessel 68, heating/pressing treatment of work-pieces is carried out, pressing/recovering process of the pressure medium gas is carried out in the other high-pressure vessel 68 to thereby enhance working efficiency of the HIP apparatus 67. The single pressing/reducing system 72 is operated relative to the two high-pressure vessels 68, and the start time of cycle motion in each high-pressure vessel 68 is shifted, thus achieving the improvement of efficiency of the HIP treatment.
However, in the technique described in the above Japanese Patent Publication No. 23484/1995, the pressure medium gas is supplied from the gas cylinder 69 to one high-pressure vessel 68 by the gas compressor 70, and afterwards, the pressure medium gas is recovered to the gas cylinder 69 from the other high-pressure vessel 68 by the gas compressor 70. Therefore, during the time when one high-pressure vessel 68 is elevated in pressure, the other high-pressure vessel 68 cannot be reduced in pressure. Accordingly, this poses a problem that the portion cannot shorten the cycle time of the HIP treatment.
It is noted that the HIP apparatus 67 described in the above Japanese Patent Publication No. 23484/1995 discloses that after termination of the HIP treatment in one high-pressure vessel 68, the valves 73 and 74 are opened to communicate both the high-pressure vessels 68 each other, whereby a high-pressure argon gas is introduced from one high-pressure vessel 68 to the other high-pressure vessel 68 to shorten the pressing time. However, there is not disclosed a method in which after pressures within both the high-pressure vessels 68 assume a balanced state, the other high-pressure vessel 68 (a high-pressure vessel supplied with the argon gas) is elevated to the HIP treatment pressure.
Further, the technique described in the above Japanese Patent Publication No. 23484/1995 for connecting in common the pressing/reducing system 72 to the plurality of high-pressure vessels 68 describes nothing about the state of temperatures within the high-pressure vessel 68. As will be carried out here, where gases are supplied at high speed making use of a pressure difference between the HIP treatment vessel in the high-pressure state and the HIP treatment vessel intended to elevate pressure thereafter, a temperature-elevating phenomenon due to so-called damming occurs whereby a temperature above the treatment chamber of the HIP treatment vessel intended to elevate pressure thereafter excessively rises. Thereby, in the control of electric power input into a heater, a temperature distribution which is difficult to control temperature occurs. In workpieces formed of a material which is difficult in temperature control, that is, variation in temperature of the workpieces becomes so great as to require heat treatment, it is difficult to secure the expected mechanical characteristics. It is impossible to avoid this problem, and it is difficult to carry out the stabilized HIP treatment to which is attached importance of uniform temperature. It is an object of the present invention to solve the aforementioned problems.